Investigators are now looking closely at the airspeed of Air France flight 447, trying to determine why it went down.

The Airbus 330 jet may not have been flying at the right speed through turbulent weather.

Aviation experts say air speed problems can be tough at times for pilots to detect.

Rescue ships are still trying to retrieve debris from the flight.

On Friday, France's transportation minister said Friday that French forces have found no evidence of the vanished jet.

He urged "extreme prudence" about suspected debris fished from the ocean.

He said the announcement by Brazilian teams that they had recovered plane debris turned out to be false.

Still missing is the plane's cockpit voice recorder and flight data recorder.

They can survive in 20,000-foot deep water for around 30 days.

A specialized mini-sub used to explore the wreckage of the Titanic will help in the search.

"Somewhere in there is a black box, in very rugged terrain at extreme depths. It's about as bad as you can make it," said Robert Ballard, who found the wreckage of the Titanic.

Meanwhile, in Rio de Janeiro, the French foreign minister joined 500 people at a cathedral to mourn the loss of their loved ones during a solemn ceremony.